doc liquidprompt#153: instructions for setting up with zsh

Merge branch 'develop' of github.com:nojhan/liquidprompt into develop

Merge branch 'master' of https://github.com/alexprengere/liquidprompt …

…into develop

Replace lptag by prompt_tag

prompt_tag is more consistent with the other prompt_* functions.

Merge branch 'develop'

correct proxy mark

add PS1 forging with liquidprompt function

This adds the possibility to forge a different prompt than the default one, by
laying out liquidprompt features in a different order.
Just build a properly escaped LP_PS1 variable.